As the sun dimmed, plants and animals gradually died.
As the asteroid that caused the extinction of the dinosaurs hit Earth, parts of the planet will fall into darkness. The years after the asteroid that led to the extinction of non-avian dinosaurs hit Earth can be called a literal "dark period." New research suggests that the smoke from the raging wildfires filled the sky and obscured the sun, which led directly to the subsequent wave of extinction.
After the asteroid impact, about 66 million years ago, the catastrophe instantly wiped out many forms of life. And the impact also caused environmental changes, leading to mass extinction over time. One of the triggers for extinction could be thick clouds full of dust and particles that erupt into the atmosphere and spread to various parts of the planet, causing parts of Earth's Earth to be shrouded in darkness and last for two years.
During that "dark period", the photosynthesis of plants may not be able to perform, which directly leads to the collapse of the ecological environment. According to research published at the annual meeting of the American Geophysical Society (AGU) in New Orleans, this decline may have continued for decades even after sunlight returned.
The Cretaceous Period (145 million to 66 million years ago) ended with a loud bang when an asteroid slammed into Earth at about 27,000 mph (43,000 km/h). It is 7.5 miles (12 km) in diameter and leaves a scar known as the Chicxulub crater, which lies underwater in the Gulf of Mexico near the Yucatan Peninsula and is at least 90 miles (150 km) in diameter. The impact eventually killed at least 75 percent of life on Earth, including all non-avian dinosaurs (the bloodline that produced modern birds is the only branch of the dinosaur family tree that has experienced extinction).
According to previous reports by Living Science, the shattered rocks and sulfuric acid clouds produced by the impact darken the sky, causing global temperatures to drop, producing acid rain and triggering wildfires. Peter Roopnarine, curator of the Geology Museum in the Department of Invertebrate Zoology and Geology at the California Academy of Sciences and a spokesman for the AGU conference, said scientists first proposed a post-cataclysmic "nuclear winter scenario" in the 1980s to describe the situation; a hypothesis that suggests darkness was one of the factors contributing to mass extinctions after Cretaceous impacts.
However, Roopnarine told Living Science in an email that researchers have only developed this model that shows how darkness can have an impact on life in about the past decade or so.
Roopnarine said: "The prevailing idea now is that global wildfires are the main source of fine soot that floats in higher atmospheres. During the first few days to weeks of a fire, the concentration of soot is high enough to block sunlight so that photosynthesis cannot proceed properly. Scientists believe that a long time ago, a giant asteroid disintegrated in the main asteroid belt between Mars and Jupiter, eventually coming to Earth, leading to the extinction of the dinosaurs.
In the study presented at the AGU conference, scientists simulated the effects of prolonged darkness by reconstructing ecological communities that might exist when an asteroid hit Earth. They used 300 species that exist, known in the Hell Creek Formation, a fossil-rich patch of shale and sandstone dating back to the late Cretaceous period and extending into parts of Montana, North Dakota, South Dakota and Wyoming.
Roopnarine said: "We focused on this area because the fossil record in this area is easy to sample and has a good understanding of ecology, so we can reconstruct paleontological communities."
They then exposed these populations to 100 to 700 days of darkness to see how long the exposure would produce the fossil record's extinction rate for vertebrates — about 73 percent. Roopnarine also mentioned in the email that the appearance of darkness after the impact will be very rapid.
The researchers found that ecosystems can recover after dark periods that last up to 150 days. But 200 days will be a tipping point. The researchers report that "after the same community experienced darkness after 200 days, some species went extinct and the dominant pattern changed." In the simulations with the longest duration of darkness, extinctions increased dramatically. According to the model, extinction levels reached 65 to 81 percent during the 650 to 700-day dark interval, suggesting that the Hell Creek community experienced a dark period of about two years.
Roopnarine added: "Environmental conditions vary around the world due to atmospheric flow and temperature variations. We estimate that the darkness may have lasted two years in the Hell Creek area, but this is only a preliminary finding. "
Once an ecosystem reaches this critical value, it will eventually bounce back as the species are new. However, the researchers found that this process takes decades. In a report at the conference, the scientists said that for communities that lasted 700 days or more, the ecosystem did not begin to rebound until about 40 years after the darkness lifted.
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